Laurie L. Wellman Ph.D. Theodore Tzavaras MD2015

Eastern Virginia Medical School

Dr. Craig Goodmurphy Anatomy Guy

1. Define discriminative touch and conscious proprioception

2. Outline the Dorsal Column, Medial Lemniscus (DCML) pathway

3. Locate each of the four neurons in the DCML pathway

4. Identify the level of decussation for the DCML pathway

discriminative touch -- the perception of location, intensity, and quality of tactile sensation (pressure, vibration, and texture)

conscious proprioception -- the appreciation of relative position and movement of the body in space

Definitions

Peripheral nerves Gracile/cunate fasciculi 1º2º neurons in the gracile/cunate nuclei Arcuate fasciculations Medial lemniscus 2º3º neurons in the VPL thalamus Post. limb of the internal capsule 3ºprimary somatosensory cortex

Crosses Midline

DC-ML Pathway

Periphery & Spinal Cord Peripheral nerve

Mechanoreceptors Pacinian corpuscle Ruffini endings Meissner corpuscle Merkel disks

Muscle spindles Golgi tendon organs

Spinal cord via dorsal root

Periphery & Spinal Cord Peripheral nerve

Cell bodies in dorsal root ganglia Pseudounipolar neurons ( ) Entry below T6 (gracile fasciculus) Entry above T6 (cuneate fasciculus)

■ ■ ■

P R + L

A

Periphery & Spinal Cord Collaterals

Somatosensory neurons are often branched

Collaterals account for reflexes & intersegmental connections

■ ■

Periphery & Spinal Cord Fasciculi

Entry below T6 (gracile fasciculus) Entry above T6 (cuneate fasciculus) Somatotopic organization (CS)

■ ■ ■

S L C

T

Brainstem Caudal medulla

Nucleus gracilis Nucleus cuneatus

1º axons synapse in nuclei Somatotopic organization (CS)

■ ■ ■

S

C

Brainstem Caudal medulla

2º axons cross in arcuate fasciculus Medial lemniscus Somatotopic organization (CS)

■ ■

S

C

S

C

Brainstem Rostral medulla

Medial lemniscus Somatotopic organization (CS)

■ ■

S

C

Brainstem Caudal pons

Medial lemniscus Somatotopic organization (CS)

■ ■

S C

Brainstem Middle pons

Medial lemniscus Somatotopic organization (CS)

■ ■

S C

Brainstem Caudal midbrain

Medial lemniscus Somatotopic organization (CS)

■ ■

S

C

Brainstem Rostral midbrain

Medial lemniscus Somatotopic organization (CS)

■ ■

S

C

Diencephalon

http://commons.wikimedia.org/wiki/File:Human_brain_frontal_(coronal)_section.JPG

Thalamus

Diencephalon Thalamus

Ventral Posterolateral (VPL) nucleus 2º axons synapse in VPL

Somatotopic organization (CS)

■ ■

http://commons.wikimedia.org/wiki/File:Human_brain_frontal_(coronal)_section.JPG

Diencephalon Thalamus

Ventral Posterolateral (VPL) nucleus Internal capsule

Posterior limb 3° axons exit VPL thalamus

■ ■

http://commons.wikimedia.org/wiki/File:Human_brain_frontal_(coronal)_section.JPG

Thalamus Ventral Posterolateral (VPL) nucleus

Internal capsule Posterior limb

3° axons exit VPL thalamus

Diencephalon ■ ■

http://commons.wikimedia.org/wiki/File:Human_brain_frontal_(coronal)_section.JPG

Forebrain Postcentral gyrus Somatotopic organization (homunculus Face+CS)

■ ■

C

S

Peripheral nerves Gracile/cunate fasciculi 1º2º neurons in the gracile/cunate nuclei Arcuate fasciculations Medial lemniscus 2º3º neurons in the VPL thalamus Post. limb of the internal capsule 3ºprimary somatosensory cortex

DC-ML Review

Don’t

Do

Don’t

Do

Try to learn all the details on your first pass.

Pay attention to orientation changes. It is uncommon for neuroanatomical features to all be seen best in the same orientation.

Limit yourself to the perspective’s we’ve shown.

Once you have the tract locations down and the decussation makes sense, add the somatotopic “fluff” details.